(a) Technical Field
The present invention relates to an end plate for a fuel cell including a sandwich insert. More particularly, it relates to an end plate for a fuel cell including a sandwich insert, in which a metal insert has a sandwich insert structure including a plurality of stacked plates, thereby securing strength and achieving a reduction in weight.
(b) Background Art
Referring to FIG. 7, in a unit cell of a fuel cell stack mounted on a fuel cell vehicle, a Membrane-Electrode Assembly (MEA) is located at the innermost side of the unit cell of the fuel cell stack. The MEA includes a solid polymer electrolyte membrane 10, through which protons pass, and catalytic electrode layers, i.e., a cathode 12 and an anode 14, coated on opposite surfaces of the solid polymer electrolyte membrane 10 such that hydrogen can react with oxygen.
Gas Diffusion Layers (GDL) 16 and gaskets 18 are sequentially stacked outside the cathode 12 and the anode 14. Separation plates 20, which include flow fields for supplying fuel and discharging water generated by the reaction, are located outside the GDLs 16.
After several hundreds of unit cells of the fuel cell stack are stacked, end plates 30 for supplying and fixing each of the unit cells are assembled at the outermost sides of the fuel cell stack.
In this case, a current collector plate for collecting electricity generated in the fuel cell stack and sending the collected electricity to the outside is mounted inside the end plates 30.
Accordingly, an oxidation reaction of hydrogen occurs in the anode 14 of the fuel cell stack, and protons and electrons are generated. At this time, the generated protons and electrons first flow to the cathode 12 through the solid polymer electrolyte membrane 10, and then to the separation plate 20. As a result, water is generated in the cathode 12 through an electrochemical reaction of the protons and electrons from the anode 14 with oxygen in the air. Electric energy is then generated through flow of the electrons and is supplied to a load requiring electric energy through the current collector plate of the end plates 30.
The end plates 30 of the fuel cell stack, which are located at opposite sides of the fuel cell stack, serve to fasten a plurality of stacked separation plates, MEAs, and GDLs, and further serve to provide a uniform surface pressure to each unit cell.
As can be seen in FIG. 6, the end plate 30 is formed from a metal insert 31, a plastic injection molded body 32, and a current collector plate 33, which are integrally formed to provide reduced weight and electric insulation.
In particular, the metal insert 31 is disposed inside an injection mold and then a plastic injection molding material is filled in the injection mold, so that the end plate 30, including the metal insert 31 surrounded by the plastic injection molded body 32, is thus formed.
The current collector plate 33 can also be disposed inside the injection mold together with the metal insert 31, and injection molded together with the plastic injection molded body 32. Alternatively, the current collector plate 33 can at a later time be separately assembled inside the plastic injection molded body 32.
The metal insert 31 of the end plate must have a high strength to resist an inner surface pressure. Accordingly, the metal insert 31 is generally manufactured through machining of a metal material, and is also typically manufactured in a complicated shape that may enhance its ability to collect generated electricity of the fuel cell stack and to fasten the fuel cell stack.
However, according to conventional methods, the metal insert of the end plate is manufactured in an integral shape, which results in a number of disadvantages.
First, in machining a lightweight material reducing structure for the metal insert, it is difficult to injection mold the metal insert. In particular, a recess or an uneven portion should not be generated on a resin surface after the injection molding of the end plates so as to prevent a fuel leak when the contact is secured with the gaskets. However, in applying the material reducing structure to the metal insert, if a thickness of the resin material of the plastic injection molded body is not uniform, a recess or an uneven portion is disadvantageously generated on the surface of the resin due to contraction of the resin. In particular, if pocket processing is performed so as to apply the material reducing structure to the integral metal insert for reducing the weight, it is difficult to uniformly maintain the thickness of the injection molding material.
Second, the integral metal insert is manufactured through cutting a metal plate or a non-metal plate through machining, so it takes a long time to manufacture the single integral metal insert. This not only makes mass production difficult, but also makes it more challenging to reduce costs.
Third, the integral metal insert should be made of a single material, so there is a difficulty in utilizing different materials for reducing weight and improving strength.